Apparatus for reproducing radio broadcasts or recorded audio frequencies



' Oct. 6, 1931. 1 D HEPBURN ET AL 1,826,173

APPARATUS FOR REPRODUCING RADIO BROADCASTS 0R RECORDED AUDIO FREQUENCIESFiled Dec. 15 1950 VI m w m 0 70 BMW 4 y Fetented @ct. 6 1.9351

and

ran "rs D'UGALD HEPBUE-N, OF TOEOIL'TO, AND MILTQIT L. TEIGMPSGN, OFEAST YORK TOWNSHIP, YORK COUNTY, ONTARIO, CANADA, ASSIGNORS TO DE FQRESTGROSLEY R ADEG GOI/IPANY, LIE-:IITED, F TORONTQ, CANADA APTPARATUS FORREPEODUGING RADIO BROADCASTS GR RECORDED AUDIO FREQUENCIES.

Application filed December 15, 1930. Serial No. 502,398.

This invention relates to radio receiving sets adapted both forreproducing radio broadcast programs, or the recorded audio frequenciesof phonographic records. When receiving radio frequencies from the airit is usual to use one or more stages of radiofrequency amplification, adetector and one or more stages of audio-frequency amplification, q butwhen audio frequencies from a record are to be reproduced one or morestages of radiofrcquency amplification are cut out. Such sets generallyemploy a tuning condenser in each stage of radio-frequency amplificationand the detector stage. Ordinarily when such a set is to be used forreproducing audio frequencies controlled by a phonographic record theconnecting wires from such an audio-frequency circuit are plugged intothe "39 grid circuit of a tube close to the output end of the set, thuscutting out one or more stages of radio-frequency amplification. At 7the same time the common practice is to open the grid circuit of thedetector or of one or more of the radio-frequency stages which removesthe corresponding condenser or condensers from the circuit or circuits.

With our new arrangement we retain the variable condenser across theinput circuit,

of the tube when such tube is connected with the audio-frequency sourcefor phonographic reproduction. which condenser forms a variablecapacitative reactance across the circuit. Also we retain in theirrespective grid circuits the tuning condensers of any stage ofamplification between the point at which the leads hereinbcfore referredto and the output end of the set. We have found that by adjusting thecondenser (or condensers) referrcd that control is secured of the ratioof reproduction of higher audio frequencies as compared with he loweraudio frequencies and tone control of the reproduction of phonographicrecords is thus obtained. When the condenser (or condensers) is set togive maximum capacitance the attenuation of the high audio frequenciesis greatest and when the condenser or condensers) is set to give minimumcapacitance the attenuation of the h' .er audio frequency is least.

The invention is illustrated in the drawing which is a diagram of partof a reproducer circuit in accordance with our invention.

1 and 2 are tubes, the plate of one being coupled with the grid of thesecond tube by the transformer 3. lhe plate of the tube 2 may beconnected with a succeeding amplifier tube or a loud speaker. The gridcircuit of the tube 2 is shunted by the variable condenser C whichordinarily forms one of a gang of tuning condensers for the diiferentstages of radio-frequency amplification and detector stage. With thegrid circuit of the tube 2 are connected wires 4 through whichaudio-frequency electrical impulses may be fed to the grid circuit. Aswitch S serves to break the normal grid circuit when phonographicrecords are to be reproduced, but the connections of the condenser Cremain unchanged. Thus when the switch S is closed and the set isreproducing radio frequencies the condenser (or condensers) serves totune the circuit across which it is connected and when the switch isopen and audio frequencies are being reproduced it serves as a tonecontrol to accentuate hi h or low frequencies of the reproduction as maybe desired.

What we claim as our invention is:

1. A radio receiving set including two vacuum tubes and a transformercoupling the plate circuit of one tube with the grid circuit of asucceeding tube; means for connecting the secondary circuit of thetransformer with an audio-frequency circuit; a switch for opening thenormal secondary circuit; and a variable condenser permanently shuntingthe grid circuit of the said succeeding tube, serving when the switch isclosed to tune the grid circuit and. when the switch is open as a tonecontrol.

2. In a radio receiving set the combination of two vacuum tubes withtheir plate and grid circuits; a transformer coupling the plate circuitof the first tube with the grid circuit of the second tube, said gridcircuit being grounded; a switch for opening and closing the gridcircuit between the secondary of the transformer and the ground; an

audio frequency circuit connected with said grid circuit at oppositesides of the switch and between the secondary of the transformer and theground; and a variable condenser connected to ground and shunting thesaid grid circuit, said condenser serving when the switch is closed totune the grid circuit and when the switch is open as a tone control.

Signed at Toronto, Canada, this 12th day of December, 1930.

DUGALD I-IEPBURN. MILTON L. THOMPSON.

